It is a tradition that started in Paris a quarter of a century ago and has since spread to major cities around Europe. New York City brought the event to the States last year. And Thursday night, for the first time ever, it came to Boston.

Close to 700 people attended at the pop-up picnic and they all had one thing in common: Until the very moment they pulled up to the Moakley Federal Courthouse, no one knew where on earth they were going.

They had all signed up for the event online, and the lucky few who were chosen to attend only got a list of rules, not the location.

They had to wear all white, pack their picnic baskets, and bring their own table and chairs. Many went above and beyond with decorations and more. Tickets cost around $30.

Late Thursday afternoon, the participants went to designated spots around Boston, where they met with their tour leaders who took them to the surprise location.

Event organizers had to turn a few hundred people away this year, but they’re already planning for next year.

They will choose a new venue – and also keep it a secret – hoping more people will be able to attend.